You're using a 216 intake manifold and it'll always leak unless you make up some stepped rings , it is far easier to just get a good used 235 intake manifold , remember the truck intake manifold has a horn mount boss on it drilled & tapped , some car intakes have the boss but it's not drilled and tapped .
How you tighten it up is important too , begin tightening in the center and work outwards .
